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Wiring regulations | 11
Types of person and
the requirements
of the Wiring
Regulations Part 2
by Jon Elliott
In the last edition of Wiring
Matters we looked at the types
of person recognised by the
Wiring Regulations, the skills
sets that they possessed and the
differences in their abilities. In
this article we will consider particular requirements within BS
7671 where the type of person
involved is of some significance.
BS EN 61140 Protection against
electric shock.
Common aspects for installa-
tion and equipment requires
that:
L hazardous-live-parts shall
not be accessible
L accessible conductive parts
shall not be hazardous live
when there is no fault or under
single fault conditions
BS EN 61140 states that those
protective measures providing
protection under normal conditions (that is, when no faults
exist) provide basic protection
and those protective measures
giving protection under single
fault conditions provide fault
protection (Section 410 refers).
The measures of protection
by automatic disconnection of
supply, double insulation and
reinforced insulation, electrical
separation to supply a single
item of equipment and extralow voltage (SELV or PELV) are
generally applicable (Regulation 410.3.3).
However, in practice automatic
disconnection of supply is
the most commonly employed method for electrical
installations while double and
reinforced insulation are more
frequently encountered in
items of equipment rather than
installations per se. Electrical
separation, SELV and PELV are
typically only applied to specific parts of an installation.
In any case, BS 7671:2008
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regulations
2.5 m
Fig: 417 Arm’s reach
2.5 m
0.75 m
requires the protective
measures mentioned above
to provide for basic and fault
protection either separately or,
in the case of enhanced protection from a single measure
(Regulation 410.3.2 refers).
0.75 m
S
1.25 m
S
•
1.25 m
S = surface expected to be occupied by persons
Basic protection
Measures for basic protection
such as basic insulation, barriers and enclosures are generally applicable and as such
may be employed in installations or parts thereof, which
are accessible to ordinary
persons - that is, which are accessible to anybody. However,
care must be taken in the use
1.25 m
I.n.,
S
liar). tool.. « .. btUer.
Fault protection
Basic insulation
Protective earthing
Barriers
Protective equipotential
bonding
Automatic disconnection in the
event of a fault
Automatic disconnection of
supply for the primary circuit
and connection of exposedconductive-parts of the
secondary circuit connected to
the protective conductor of the
primary circuit of the source
Placing out of reach
Supplementary insulation
Reinforced insulation
Simple separation
Non-conducting location
Earth-free local equipotential
bonding
IET Wiring Matters | Spring 10
it"tI!.
'0\;11 4 '11 ftl)' .1....."U,oI..... o;l. t: ~
Basic protection
Obstacles
The values refer to bare hands
without any assistance, e.g.
from tools or a ladder.
Tlle \;t1I5t!" II!"-t'''lot h:.1!
The following protective methods are recognised in BS 7671:
Enclosures
limit of arm's reach
of the measures of obstacles
and placing out of reach to
prevent access of persons (or
indeed livestock) with live parts
as both measures may be
deliberately or in some cases
unintentionally circumvented
(Regulation 417.2). Because
of this, the use of these two
methods is restricted to installations, or parts thereof, which
can only be accessed by
skilled persons or instructed
persons under the supervision
of skilled persons (Regulations
410.3.5 and 417.1)
To be effective an obstacle
(as defined) should prevent
unintentional bodily approach
to, and contact with, live parts
during the normal operation
and use of the equipment in
question (Regulation 417.2.1).
However an obstacle may be
readily removable without the
use of a key or tool (Regulation
417.2.2).
Placing out of reach requires
a designer to ensure that
simultaneously accessible
parts at different potentials
are not placed within arm’s
reach (Regulation 417.3.1).
Arm’s reach is considered to
span 1.25 m horizontally and
2.5 m vertically as shown in
figure 417 of BS 7671:2008
which is reproduced above.
However this does not take into
account the use of ladders or
work involving long conducting
objects and tools and so the
use of such within areas where
basic protection is provided by
placing live parts out of reach
should the subject of serious
consideration.
In the case of items of street
furniture, basic protection may
only be provided by placing
out of reach where the item
in question is situated more
than 1.5 m from a low voltage
overhead line unless the maintenance of said equipment is
only to be carried out by skilled
persons (Regulation 559.10.1).
Wherever the use of either obstacles or placing out of reach
is employed it is necessary to
provide the required equipment, instruction and training
to allow the skilled persons and
the instructed persons under
their supervision to be able
to work safely. As such, those
parts of an installation where
such measures are employed
should be clearly identified
by the posting of notices and
measures, such as, securing
with locks and permit-to-work
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Wiring regulations | 13
systems should be put in place
to control access and work
activities undertaken therein.
When a designer is considering
the use of obstacles or placing
out of reach to provide basic
protection, it is strongly recommended that careful consideration be given to the statutory
requirements relating to:
L system, work activities and
work equipment (Regulation 4
of the Electricity at Work
Regulations 1989 - EWR)
L insulation, protection and
placing of conductors (Regulation 7 of EWR)
L work on or near live conductors (Regulation 14 of EWR)
L Earthing or other suitable
precautions (Regulation 8 of
EWR)
L working space, access and
lighting (Regulation 15 of
EWR), and
L persons to be competent
to prevent danger and injury
(Regulation 16 of EWR)
Considerable guidance in
support of these regulations
can be found in Memorandum
of guidance on the Electricity at Work Regulations 1989
(HSR25) published by the
Health and Safety Executive
and available as a free download from the HSE website.
Fault protection
In the case of automatic
disconnection of supply
(ADS), fault protection is
provided through the provision
of protective earthing, protective equipotential bonding
and automatic disconnection
in the event of a fault including, where applicable additional protection (Regulation
411.10).
Additional protection by means
of an RCD with a rated residual
operating current not exceeding 30 mA and giving an
operating time not exceeding
40 ms at a residual current
of 5 IΔn should be provided
for socket-outlets not exceeding a rating of 20 A intended
for general usage by ordinary
persons, and for mobile equipment of rating less than 32 A
that will be used outdoors
(411.3.3). A relaxation of this
requirement is however permitted for socket-outlets which will
be used, in for example, those
industrial and commercial installations where work activities
are under the effective control
of skilled or instructed persons
and the work activities taking
place do not of themselves
make RCD provision essential.
This issue will be considered
in further detail later in this
article.
Where functional extra-low
voltage is employed, it is
necessary to connect the
exposed-conductive-parts of
the equipment so supplied to
the protective conductor of the
primary circuit of the source
in addition to those protective
measures required for ADS
(Regulation 411.7.3)
In the case of an accessible
enclosure forming part of street
furniture it should only be possible to gain access to the live
parts within by the use of a key
or a tool, unless said enclosure
is so located that only skilled
or instructed persons have access (Regulation 559.10.3.1).
Where isolation and switching
operations on street furniture
supplied from a TN supply are
intended only to be carried out
by, at the least, instructed persons and where the necessary
precautions have been taken
to prevent said equipment from
being re-energised prematurely
in a manner that could give
rise to danger, it is acceptable
for switching on-load and isolation to be achieved by removal
of the distributor’s fuse therein.
Cables concealed in walls
It has long been a requirement
of the Wiring Regulations that
where cables are concealed in
walls or partitions at a depth
of less than 50 mm from the
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regulations
150 mm
150 mm
devices should comply with
the relevant parts of BS EN
60439-3.
150 mm
Insulation monitoring devices
150 mm
Room 2
no protection required
Room 1
surface that they either:
L incorporate an earthed me-
tallic covering such as armouring or sheath, or
L be enclosed in an earthed
conduit, trunking or duct, or
L be otherwise protected against
penetration by nails, screws
and the like by the addition of
mechanical protection, or
L be installed in the safe zones
as shown in the diagram below
(Regulation 522.6.6)
In the case of an installation
not under the supervision of
a skilled or instructed person
the 17th Edition has introduced a requirement that an
RCD having a rated residual
operating current not exceeding 30 mA and meeting
the conditions contained in
Regulation 415.1.1 must be
installed to provide additional
protection where an insulated and sheathed or similar
type cable is run in the safe
zones without any other form
of mechanical protection. A
similar requirement has also
been introduced for situations where such cables are
installed in partitions formed in
part from metallic components
(Regulation 522.6.8 (v)). So,
additional protection by means
of an RCD as described above
would be required for domestic
premises. Additional protection
may also be required in some
commercial or industrial instal-
IET Wiring Matters | Spring 10
protection required unless
depth greater than 50 mm
lations irrespective of whether
they are under the supervision of
a skilled or instructed person as
Regulation 6 of the EAWR 1989
requires electrical equipment to
be of such construction or
otherwise suitably protected to
prevent dasnger. This can be the
provision of RCDs where the
environment of use increases the
risk of sustaining an electric
shock. Wet working environ
ments, such as those in kitchens,
are an example of where this
would apply.
RCDs and circuit-breakers
RCDs powered from an independent auxiliary source and
which do not operate automatically in the event of a failure
of the auxiliary source may
only be used in an installation
if either fault protection is still
maintained in the event of loss
of the auxiliary source or the
installation is under the control
of a skilled or instructed person
and regularly inspected/tested
by a person competent in such
work (Regulation 531.2.6).
Where an RCD can be accessed
and operated by one other than
a skilled or instructed person
(that is, therefore, an ordinary
person) it should be of a type
where it is not possible to effect
any changes or adjustments to
the settings for its operational
sensitivity or time delay thereof
without the use of a key or tool
(Regulation 531.2.10). A similar
requirement exists relating to
the modification or adjustment
of the overcurrent settings of
circuit-breakers (Regulation
533.1.2).
Isolators, switchgear and
controlgear
Regulation 537.1.2 states that
the neutral conductor in a TN-S
or TN-C-S system need not be
isolated and switched. Where
a link is inserted in the neutral
conductor, it should not be possible to remove the link without
the use of a key or tool and/or
it should be placed so that is
accessible to skilled persons
only (Regulation 537.2.2.4).
Any main switch intended to be
operated by ordinary persons
should disconnect both poles of
a single-phase supply (Regulation 537.1.4).
Where a single-phase
installation having a supply
rated at 100 A or less such
as the majority of domestic
premises is to be left under the
control of ordinary persons,
the switchgear and controlgear
therein should either comply
with the requirements given
in BS EN 60439-3 Particular
requirements for low-voltage
switchgear and controlgear
assemblies intended to be
installed in places where unskilled persons have access to
their use. Distribution boards.
In the case of a consumer unit,
the constituent component
parts including the protective
It is a requirement in installations supplied from an IT system
that an Insulation monitoring
device (IMD) is installed to
continuously monitor the insulation resistance of the complete
system including and extending
beyond the secondary side of
the source of supply (Regulation
538.1.1) to indicate when a first
fault occurs between a live part
and an exposed-conductive-part
or between a live part and Earth
(Regulation 411.6.3.1). Where
such devices are located in
positions accessible by ordinary
persons - that is persons who
are neither skilled nor instructed
- the IMD should be so designed
or installed such that the use
of a key, tool or password is
required before changes can
be made to operational settings
(Regulation 538.1.3).
Storage batteries and safety
sources
Storage batteries are commonplace in most industrial and
commercial installations either to
provide a back-up supply as is
the case with fire and security alarm systems, emergency
lighting and uninterruptible
power supply (UPS) systems
or to provide a source of supply
independent of that derived
from the public distribution
network to supply, for example,
compressors designed to run
standby generation up to speed
in the event of supply failure.
Batteries may present a shock
risk and flammable gases may
be released in normal use. In
both cases ordinary persons
may not be aware of the risks
that may exist. As a result batteries forming part of an installation
should be so placed that they
are only accessible to skilled or
instructed persons (Regulation
551.8.1).
A safety source for a safety
service, whatever its nature
(Regulation 560.6.2), and
The protective bonding conductors associated
with the electrical installation in this location
MUST NOT BE CONNECTED TO EARTH.
Equipment having exposed-conductive-parts
connected to earth must not brought into this
location.
any associated switchgear
and controlgear (Regulation
560.7.5) should also be in a location only accessible to skilled
or instructed persons.
Fault protective measures subject to supervisory restrictions
Moving away from protection
by ADS, Regulation 410.3.6
permits non-conducting
location, earth-free local
equipotential bonding and
electrical separation for
the supply to more than one
item of current using equipment to provide fault protection
but only where the installation,
or more realistically, that part
thereof protected by such
measures, remains under
the supervision and effective
control of skilled or instructed
persons (Section 418).
herent or applied, of extraneous-conductive parts (nonconducting location 418.4)
L the resistance of insulating
walls and floors within the location when tested in accordance with the requirements
of Regulation 612.5.1 should
not exceed the values given
in Appendix 13 appropriate
to the particular test method
employed (non-conducting
location - Regulation 418.1.5)
All of the above requirements
need to be present for the
measure to be effective. This is
why it is so important that effective control and supervision
of the location so protected is
maintained. If inadequately
supervised, the measure can
be rendered ineffective and
therefore potentially dangerous
by the introduction of class I
items of mobile equipment or
The protective measure of
non-conducting location is very indeed extraneous-conductive
parts. Moreover, persons
seldom used within the United
Kingdom but a summary of the placed in control of a location
so protected will need to
requirements relating to its use
ensure that excessive humidity
is given below:
does not reduce the insulation
resistance of the floors and
L It should not be possible unwalls of the location beyond
der normal operating conditions
acceptable levels (Regulation
for persons to be able to make
418.1.6).
simultaneous contact between
The responsible person must
L two exposed-conductivealso ensure that no potentials
parts, or
L an exposed-conductive part which might give rise to danger
and an extraneous-conductive are allowed to appear beyond
the location from within (Regupart
lation 418.1.7)
where such parts can be at
different potentials (Regulation
418.1.2)
Protection by earth-free local
L no protective conductors
equipotential bonding is a fault
should extend into the location
protection measure which can
so protected (Regulation 418.1.3) only realistically be applied to a
particular area or location within
L exposed and extraneousthe greater installation. In order
conductive parts are deemed
for this protective measure to be
to be adequately separated
effective all exposed and extrathrough
L the relative spacing between neous-conductive parts within
the location must be electrically
them being not less than 2.5
m or 1.25 m if placed beyond separate from earth or other
potentials being introduced from
arm’s reach
outside (Regulation 418.2.3)
L the placing of obstacles
between exposed and extrane- and, if simultaneously accessible, be connected together by
ous-conductive parts
local protective bonding conducL the insulation, whether in-
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Wiring regulations | 15
tors (Regulation 418.2.2). The
accessible floor surface within
such a location may be constructed of non-conducting materials or from a conductive floor
connected to the local earth-free
bonding within the location and
wholly insulated from Earth.
A particular risk of shock
can exist at the point where
persons pass into the earthfree protected area from the
greater, earthed, installation
and so effective supervision
at this point must be maintained to ensure that precautions such as insulating mats
or floor panels at the point
of transition are not removed
and remain in a serviceable condition (Regulation
418.2.4). Other potential risks
arising from persons unfamiliar with the method of protection being employed are that
during the course of alterations, additions, maintenance
or repair work a connection to
earth is introduced into the
location or that portable and/
or handheld tools or
equipment having exposed
conductive parts are used in
the location whilst connected
to the earthed supply within
the “normal” installation. In
the hope of preventing this
from occurring it is a requirement that the warning notice
reproduced above (Regulation
514. 13.2) is posted at any
and all points of entry to the
location protected by earthfree local equipotential bonding (Regulation 418.2.5).
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The use of a supply from a TN
system can introduce an earth
into the location via the earthed
neutral conductor. As a result
the supply to a location where
earth-free local equipotential
bonding is used as a protective
measure is most likely to be
taken from a source employing
electrical separation.
Electrical separation for the
supply to more than one item
of equipment is a protective
measure so arranged that a
single fault or first fault should
not present a risk of electric
shock occurring. However as
the presence of such a fault
is unlikely to be detected
in normal use a potentially
dangerous situation could arise
if further faults were to occur.
As a result it is a requirement
for the separated circuit to be
so arranged as to minimise the
risk of damage or insulation
failure occurring (Regulation
418.3.3).
All exposed-conductive parts
associated with the separated
circuit are required to be connected together by nonearthed, insulated protective
bonding conductors and no
connection should be made
from the exposed-conductive
parts so bonded to the protective conductor, exposed-conductive parts of other circuits,
or any extraneous-conductive
parts within the location
(Regulation 418.3.4) and the
protective conductor contact
of socket-outlets are to be connected to the bonded exposedconductive parts (Regulation
418.3.5).
Again it can be seen that effective supervision must be
IET Wiring Matters | Spring 10
provided to ensure that the
above requirements are not
deliberately or accidentally
defeated rendering the method
of protection ineffective.
Special installations and locations
To be included in Part 7 of
BS 7671 a location or type of
installation should present an
increased risk of shock to persons (or livestock) either by its
nature or from how it is used.
To illustrate this, a construction
site is a harsh environment
for an electrical installation,
and the likelihood of damage
occurring to wiring systems
and equipment is, relatively
speaking, high. As a result,
special measures are required
to ensure that the installation
is sufficiently robust. In the
case of a swimming pool the
increased risk of shock is as a
direct result of factors such as
the lack of dry (and therefore insulating) footwear and
clothing and the significantly
reduced resistance of skin
when wet. A number of installations or locations covered by
Part 7 are subject to specific
requirements related to the
types of person recognised by
BS 7671.
Where extra-low voltage transformers are employed in an
electrical installation forming
part of an exhibition, show or
stand falling within the scope
of Section 711, the transformers should be so placed that
they are not within arm’s reach
of members of the public (that
is, ordinary persons as defined) and such that they can
be accessed to facilitate testing
and maintenance by skilled
persons competent in such
work (Regulation 711.55.6).
Some types of mobile and
transportable unit are capable
of being connected to a wide
range of potential supplies.
However hazardous situations may arise from loss of
continuity of the connection to
the source of earth, an open
circuit on a PEN conductor (as
defined) resulting in a diverted
neutral current or if the unit
contains much electronic
equipment a potentially harmful functional current being
present on earthed metalwork. As a result, regulation
717.411.4 states that:
L a suitably skilled or in-
structed person has confirmed
the suitability of the means of
earthing prior to connection ,
and that
L a mobile or transportable
unit may only connected to a
supply derived from a TN-C-S
system where the unit remains
under continuous supervision by a skilled or instructed
person whilst in use, it being
their responsibility to confirm
the effectiveness of the means
of earthing for the unit whilst it
is in use.
Where safety isolating transformers are employed in a temporary
installation within a fairground,
amusement park or circus they
should be mounted out of arm’s
reach or failing that, installed
such that they are only accessible to skilled or instructed
persons. Moreover, there should
be adequate means of access
to permit inspection, testing
and maintenance (Regulation
740.55.5) and with the exception of those items intended for
operation by ordinary persons,
all switchgear and controlgear
should be placed inside enclosures which can only be opened
by the use of a key or a tool
(Regulation 740.51).
Inspection and testing
In the case of most types
electrical installation there is
no statutory requirement to
carry out inspection and testing periodically. It is, however,
a commonly adopted practice
seen as a means of meeting
the maintenance obligations
given in, for example, the
Electricity at Work Regulations 1989 (Regulation 4)
and the Housing Act 1985
(Section 11). BS 7671 is in
the most part concerned with
the design, installation, and
initial inspection and testing of new installations but
Chapter 62 contains a number
of requirements relating to
periodic inspection and testing.
Regulation 622.2 states that
periodic inspection and testing
is not required where an installation is under an effective
management system operated
by skilled persons covering its
maintenance. However, and as
has been mentioned previously, the persons responsible may
be held accountable in the
event of an incident occurring.
As such, appropriate records
must be kept of the maintenance activities undertaken.
Useful reading
Guidance Note 2 – Isolation and
switching. Published by the IET
Guidance Note 5 – Protection
against shock. Published by
the IET
HSR 25 – Memorandum of
guidance on the Electricity
at Work Regulations 1989.
Published by the HSE
HSG 85 – Electricity at work.